It is often useful to be able to predict the fertility of a mammalian male animal in a variety of contexts. For example, animal breeders typically go to great lengths to find male animals likely to produce offspring having desirable genetic traits. However, animal breeding is often an expensive endeavor and males having low fertility are of reduced value due to the increased cost of breeding the animal where repeated inseminations are required to ensure impregnation. Currently, there are few reliable methods for detecting a lack of fertilizing capacity in these male animals short of statistical data compiled on their past breeding results.
Additionally, the medical community is often concerned with human fertility but has few reliable methods for evaluating the fertility of male patients. In particular, physicians have few reliable methods for detecting a lack of capacitation in the sperm of a patient.
Mammalian spermatozoa in semen cannot fertilize eggs but must undergo alterations in the plasma membrane in order to acquire fertilizing capability. The process during which the spermatozoa undergo these alterations in their membrane is termed capacitation and occurs naturally in the female reproductive tract once the sperm has been deposited.
Capacitation refers to the ability of sperm to adhere to, penetrate and fertilize susceptible ova. Penetration and fertilization not only requires potentiality of the sperm to achieve a functional status but also requires that favorable conditions exist in the uterine environment. If favorable conditions exist in the mammalian uterus, sperm become capacitated, penetrate the ova and embryonic development begins.
It has recently been discovered that certain synthetic fibronectin-derived polypeptides containing the tripeptide, Arginine-Glycine-Aspartate, in their cell binding domains will competitively inhibit sperm-oolemal adhesion and penetration of hamster ova contacted with either human or hamster sperm that has undergone successful capacitation. Further evidence has been obtained that receptors for proteins, such as fibronectin, which contain the tripeptide, Arg-Gly-Asp, exist on the surface of mammalian eggs. Consequently, it has been postulated that fibronectin expression on the spermatozoan surface might play an important role in the adhesion and penetration of sperm to susceptible ova. Previously, the nature of the role of fibronectin has remained unclear.
Fibronectin plays a wide role in diverse processes, ranging from immune adherence of microbes to connective tissue remodelling and embryogenesis. For example, fibronectin has been found in heavy accumulations in vivo at sites of tissue inflammation and injury. Fibronectin is a high molecular weight glycoprotein homodimer, consisting of two identical chains (Mr=220-250,000), connected by disulfide bridges which can exist in two forms, plasma fibronectin, which is soluble, and cellular fibronectin, which is insoluble. Limited proteolytic digestion of cellular fibronectin has revealed several domains with different binding affinities for collagen, fibrinogen and heparin, in addition to the cell binding domain. The cell binding domain of fibronectin, as well as other extracellular matrix proteins such as collagen Type I, Type IV and laminin, have been shown to possess the tripeptide sequence previously mentioned, Arginine-Glycine-Aspartate.
It has now been discovered that there is significant increase in the presence of fibronectin on the surface of capacitated mammalian sperm as compared with fresh mammalian sperm which has not undergone capacitation. As a result, it has now been postulated that detecting the presence of fibronectin expressed upon the surface of the sample of mammalian sperm is a good indicator of whether the sperm has undergone successful capacitation.
It is therefore an object of the present ineention to provide an improved method for detecting the presence of infertility in a mammalian male test animal using antibodies to fibronectin.
It is a further object of the present invention to provide a method for detecting a lack of capacitation in a sample of sperm from a mammalian male test animal using antibodies to fibronectin.
Finally, it is an object of the present invention to provide a method for using fibronectin antibodies to detect a lack of capacitation in a sample of human spermatozoa due to disorders related to fibronectin expression on the sperm surface.